1. Field of the Invention
This invention relates to diagnosing reciprocating internal combustion engines electronically.
2. Description of the Prior Art
It is known in the prior art to analyze the starter current magnitude of an engine while being cranked by an electrical starter motor in order to determine the relative compression of the various cylinders. In one such apparatus known to the art, the starter current waveform is simply plotted as a function of time on a well known chart recorder, and the magnitudes plotted thereon are compared to provide a relative indication of individual cylinder compressions. In a more sophisticated apparatus known to the art, magnitude of starter current is sampled frequently, and the sampled data is analyzed electronically to determine the swings in starter current which relate in some fashion to the individual cylinders. In spark ignition engines, the analysis can be performed by synchronization with the electrical spark control system (the distributor and so forth) on a cylinder by cyclinder basis. However, this system has been found to have shortcomings, particularly in analyzing engines which have gross problems, in which the electrical timing may in fact be significantly displaced from its desired relationship to the crankshaft, which fact is not apparent until diagnosis is complete; obviously, diagnosis which assumes a certain degree of health is less useful than that which does not. Further, such systems are totally useless in engines which do not utilize spark ignition.